Detection of resynchronization markers when decoding an MPEG-4 bitstream

1. A method of detecting a resynchronization marker in an encoded MPEG-4 video bitstream, the method comprising: at a macroblock boundary between first and second video packets in a video object plane (VOP) in the video bitstream, checking the video bitstream for a valid sequence of stuffing bits, wherein the VOP is a bi-directionally coded type of VOP; based on the VOP being the bi-directionally coded type of VOP, computing a first candidate resynchronization marker length for the second video packet based on a first version of MPEG-4 Visual; based on the VOP being the bi-directionally coded type of VOP, computing a second candidate resynchronization marker length for the second video packet based on a second version of MPEG-4 Visual; in the second video packet, checking the video bitstream for a first valid resynchronization marker bit sequence having the first candidate resynchronization marker length; in the second video packet, checking the video bitstream for a second valid resynchronization marker bit sequence having the second candidate resynchronization marker length; and without an indication of which of the first and second versions of MPEG-4 Visual was used for encoding the video bitstream, detecting the resynchronization marker in the second video packet, in response to detecting: the valid sequence of stuffing bits in the video bitstream; and one of the first and second valid resynchronization marker bit sequences in the second video packet.

2. The method of claim 1 , wherein computing a first candidate resynchronization marker length and computing a second candidate resynchronization marker length are performed in parallel.

3. The method of claim 1 , wherein the first version is version two or version three of MPEG-4 Visual, and the second version is version one of MPEG-4 Visual.

4. The method of claim 1 , wherein: computing a first candidate resynchronization marker length comprises: computing the first candidate resynchronization marker length as eighteen when a value of an fcode is less than three; and computing the first candidate resynchronization marker length as a sum of sixteen plus the value of the fcode when the value of the fcode is greater than or equal to three; and computing a second candidate resynchronization marker length comprises: computing the second candidate resynchronization marker length as a sum of sixteen plus the value of the fcode; wherein the value of the fcode is the larger of vop_fcode_backward and vop_fcode_forward.

5. A video decoder for decoding an encoded MPEG-4 video bitstream, wherein the decoding comprises detecting a resynchronization marker in the encoded MPEG-4 video bitstream, and wherein the detecting comprises: at a macroblock boundary between first and second video packets in a video object plane (VOP) in the video bitstream, checking the video bitstream for a valid sequence of stuffing bits, wherein the VOP is a bi-directionally coded type of VOP; based on the VOP being the bi-directionally coded type of VOP, computing a first candidate resynchronization marker length for the second video packet based on a first version of MPEG-4 Visual; based on the VOP being the bi-directionally coded type of VOP, computing a second candidate resynchronization marker length for the second video packet based on a second version of MPEG-4 Visual; in the second video packet, checking the video bitstream for a first valid resynchronization marker bit sequence having the first candidate resynchronization marker length; in the second video packet, checking the video bitstream for a second valid resynchronization marker bit sequence having the second candidate resynchronization marker length; and without an indication of which of the first and second versions of MPEG-4 Visual was used for encoding the video bitstream, detecting the resynchronization marker in the second video packet, in response to detecting: the valid sequence of stuffing bits in the video bitstream; and one of the first and second valid resynchronization marker bit sequences in the second video packet.

6. The video decoder of claim 5 , wherein computing a first candidate resynchronization marker length and computing a second candidate resynchronization marker length are performed in parallel.

7. The video decoder of claim 5 , wherein the first version is version two or version three of MPEG-4 Visual, and the second version is version one of MPEG-4 Visual.

8. The video decoder of claim 5 , wherein: computing a first candidate resynchronization marker length comprises: computing the first candidate resynchronization marker length as eighteen when a value of an fcode is less than three; and computing the first candidate resynchronization marker length as a sum of sixteen plus the value of the fcode when the value of the fcode is greater than or equal to three; and computing a second candidate resynchronization marker length comprises: computing the second candidate resynchronization marker length as a sum of sixteen plus the value of the fcode; wherein the value of the fcode is the larger of vop_fcode_backward and vop_fcode_forward.

9. A system, comprising: at least one processor; and at least one memory storing instructions executable by the processor for detecting a resynchronization marker in an encoded MPEG-4 video bitstream, wherein the detecting comprises: at a macroblock boundary between first and second video packets in a video object plane (VOP) in the video bitstream, checking the video bitstream for a valid sequence of stuffing bits, wherein the VOP is a bi-directionally coded type of VOP; based on the VOP being the bi-directionally coded type of VOP, computing a first candidate resynchronization marker length for the second video packet based on a first version of MPEG-4 Visual; based on the VOP being the bi-directionally coded type of VOP, computing a second candidate resynchronization marker length for the second video packet based on a second version of MPEG-4 Visual; in the second video packet, checking the video bitstream for a first valid resynchronization marker bit sequence having the first candidate resynchronization marker length; in the second video packet, checking the video bitstream for a second valid resynchronization marker bit sequence having the second candidate resynchronization marker length; and without an indication of which of the first and second versions of MPEG-4 Visual was used for encoding the video bitstream, detecting the resynchronization marker in the second video packet, in response to detecting: the valid sequence of stuffing bits in the video bitstream; and one of the first and second valid resynchronization marker bit sequences in the second video packet.

10. The system of claim 9 , wherein computing a first candidate resynchronization marker length and computing a second candidate resynchronization marker length are performed in parallel.

11. The system of claim 9 , wherein the first version is version two or version three of MPEG-4 Visual, and the second version is version one of MPEG-4 Visual.

12. The system of claim 9 , wherein: computing a first candidate resynchronization marker length comprises: computing the first candidate resynchronization marker length as eighteen when a value of an fcode is less than three; and computing the first candidate resynchronization marker length as a sum of sixteen plus the value of the fcode when the value of the fcode is greater than or equal to three; and computing a second candidate resynchronization marker length comprises: computing the second candidate resynchronization marker length as a sum of sixteen plus the value of the fcode; wherein the value of the fcode is the larger of vop_fcode_backward and vop_fcode_forward.